Machinists recognize that "broaching" is a method of machining metallic workpieces whereby successive levels of metal are removed by a multi-toothed tool called a broach. The broach is either pushed or pulled across a surface of the workpiece in order to cut away the metal and impart the desired configuration to the surface upon which the machining operation is performed.
Broaching machines are, however, typically quite expensive, and substantial fixtures are required to secure the workpiece during the broaching operation. The fixture itself must not deflect, or move, under the cutting pressures, which are quite high, and the clamping means by which the workpiece is secured to the fixture must also ensure that the workpiece will not slip during the broaching operation, even if unusually heavy loads are encountered, such as would result from attempting to excise too substantial a layer of metal or from cutting through a hard spot. Any slippage of the workpiece during the broaching operation would not only jeopardize the workpiece but could also break one or more teeth on the broach or even break the broach itself.
Broaching fixtures are also employed to effect accurate positioning of the workpiece relative to the broaching machine, and, for some machining operations, to effect indexing of the workpiece and even to provide a means by which to move the workpiece into and out of cutting position and thereby assure a more convenient access for mounting and demounting of the workpiece relative to the fixture.
There are both push-type and pull-type broaching machines. With either variety access to both sides of the workpiece is mandatory, and particularly when machining the boundary surface of an aperture through the workpiece.
With the pull-type broaching machine the broach must be positioned on one side of the workpiece so that a front pilot on the broach can be inserted into the aperture of the workpiece that is to be machined, with the shank of the broach extending through the aperture for connection to the pull head of the broaching machine located on the opposite side of the workpiece. The broaching machine then pulls the broach through the aperture in the workpiece to effect the desired machining operation upon the boundary surface of the aperture.
Even on the push-type broaching machines access is required to both sides of the workpiece. With the push-type broaching machine the front pilot is on the opposite end of the broach, and both the broach and the front pilot are initially on the same side of the workpiece as the broaching machine itself. After the machining operation is completed, however, the broach must be disconnected from the broaching machine and removed from the opposite side of the workpiece, because the broach must never be moved through the workpiece back to the starting position.
In view of even the brief requirements discussed above it becomes apparent that heretofore known broaching machines, and the requisite fixtures, are not readily taken into the field for set up on the job site. Moreover, there is no known broaching apparatus that is capable of machining the boundary surface of an aperture in a workpiece without having full access to both sides of the workpiece.